Bio-safety assessment of carbon quantum dots, N-doped and folic acid modified carbon quantum dots: A systemic comparison

The carbon quantum dots (CQDs) and their functionalized materials are promising in biomedical field because of their unique properties; meanwhile, a growing concern has been raised about the potential toxicity of these modified materials in biosystem. In this study, we synthesized original CQDs and two common functionalized CQDs including N-doped CQDs (NCQDs) and folic acid-modified CQDs (FA-CQDs), and compared the toxicity and biocompatibility with each other in vitro and in vivo. L929, C6 and normal cell MDCK were selected to detect the adverse reaction of these materials in vitro. No acute toxicity or obvious changes were noted from in vitro cytotoxicity studies with the dose of these CQD materials increasing to a high concentration at 1 mg/mL. Among these materials, the FA-CQDs show a much lower toxicity. Moreover, in vivo toxicity studies were performed on the nude mice for 15 days. The experimental animals in 10 or 15 mg/kg groups were similar with animals treated by phosphate buffer solution (PBS) after 15 days. The results of the multifarious biochemical parameters also suggest that the functionalized products of CQDs do not influence the biological indicators at feasible concentration. Our findings in vitro and in vivo through toxicity tests demonstrate that CQDs and their modified materials are safe for future biological applications.